The present invention relates to a method for warning the deflation of tires and a system thereof, and a judgment program of the deflation of tires. More particularly, the present invention relates to a method for warning the deflation of tires which can detect the deflation of 2 wheels at the same axle, the simultaneous deflation of 4 wheels or the abrasion of tires and a system thereof, and a judgment program of the deflation of tires.
A detection system of the deflation of tires in an indirect system has conventionally used a principle that since the outer diameter of a tire (the dynamic loading radius of a tire) is reduced more than that of a tire having a normally prescribed pressure (normal internal pressure) when the tire is deflated, rotational angular velocity (wheel speed) is increased as compared with other normal tires. For example, a method of detecting the deflation from the relative difference of the rotational angular velocity of a tire uses as a judgment value;DEL={(F1+F4)/2−(F2+F3)/2}/{(F1+F2+F3+F4)/4}×100(%)(for example, refer to Japanese Unexamined Patent Publication No. 305011/1988)).
Wherein F1 to F4 are the rotational angular velocities of a front left tire, a front right tire, a rear left tire and a rear right tire, respectively.
However, since the method judges the deflation from the difference of mutual sums of the rotational angular velocities of the diagonals of 4 wheels, the simultaneous deflation of 2 wheels at the same axle and the naturally simultaneous deflation of 4 wheels could not be judged.
Consequently, the applicant proposed previously a method of detecting deflation of tires and a system thereof which can detects at least the deflation of driving wheel tires, in an indirect system using the rotational information of tires (refer to Japanese Unexamined Patent Publication No. 211925/2003).
The method described in Japanese Unexamined Patent Publication No. 211925/2003 comprises a step of detecting the rotational information of tires, a step of respectively calculating and storing wheel speeds, vehicle accelerations, slip ratios of front and rear wheels, a traveling distances and radius of traveling circle from the rotational information of respective tires, a step of calculating moving average of the vehicle acceleration and the slip ratios of front and rear wheels, a step of accumulating the traveling distance and the vehicle acceleration and the slip ratios of front and rear wheels which were transfer-averaged when the above-mentioned radius of traveling circle are a fixed value or more, a step of determining correlation coefficients with the mutual regression coefficients of the above-mentioned vehicle accelerations and the slip ratios of front and rear wheels when the accumulated traveling distances are a fixed distance or more, a step of determining whether the pressures of at least driving wheel tires are decompressed or not, by comparing the judgment value of said regression coefficients with the internal pressure reference value of regression coefficients which were preliminarily calculated by the above-mentioned step at the reference internal pressure of tires as the judgment value of regression coefficients when said correlation coefficients are a fixed value or more and a step of warning deflation of tires based on the result of said deflation judgment. In the method, the vehicle accelerations and the slip ratios based on the wheel speeds of 4 wheel tires utilizing that relation between the vehicle accelerations and the slip ratios is varied when the internal pressures of driving wheel tires are reduced, and the simultaneous deflation of one driving wheel tire or left and right driving wheel tires and the like are judged from the time dependent movement of the mutual regression coefficients.
However, since the above-mentioned method described in Japanese Unexamined Patent Publication No. 211925/2003 detects substantially the deflation of driving wheels, it cannot detect the deflation of only following wheels. Further, even if the pressures of the driving wheels are reduced, the relation of the vehicle accelerations with the slip ratios which are used as the judgment reference of deflation shows the similar tendency as a case that tires were worn; therefore it must be judged from the use duration and traveling distances of tires whether the tires are deflated or whether tires are worn. Accordingly, the method described in Japanese Unexamined Patent Publication No. 211925/2003 has a constitution that an warning for examining the air pressures of tires is carried out when an initialization switch was not operated for a fixed term, or when the total traveling distances until the initialization switch is operated again after operating the initialization switch reaches at a fixed distance.